We have a lot of abstraction that isn't really needed. This patch
removes some of that abstraction and reorganizes the code accordingly.
- Merged storage and sqlalchemy folders.
- Deprecated [central].storage_driver.
- Minor cleanup to SQL code.
- Cleaned up comments and unit tests.
Change-Id: I8f0508aedcc028b1a6e74c790c5d757a0d6c98d7
0c30fc491b